Tissues deprived of blood and oxygen undergo ischemic necrosis or infarction with possible irreversible organ damage. In some circumstances, such as during surgery, interruption of blood flow resulting in ischemia of some organ is unavoidable. In addition, in the case of solid tumors, it is desirable to interrupt the blood flow and actually induce ischemia. Once the flow of blood and oxygen is restored to the organ or tissue (reperfusion), the organ does not immediately return to the normal preischemic state. For example, in the case of the ischemic myocardium, reperfused postischemic non-necrotic myocardium is poorly contractile and has reduced concentrations of high energy nucleotides, depressed subcellular organelle function and membrane damage that resolves only slowly.
Mitochondrial aldehyde dehydrogenase-2 (ALDH2) is encoded in the nuclear genome and is transported into mitochondria. ALDH2 is a tetrameric protein composed of four identical subunits, each consisting of 500 amino acid residues. This tetramer can be regarded as a dimer of dimers. The interface between monomers that form a dimer is different and more extensive than the interface between the two dimers that form the tetramer. Each subunit is composed of three main domains: the catalytic domain, the coenzyme or NAD+-binding domain, and the oligomerization domain.